There is a current trend towards high-power wireless energy transfer systems for charging handheld devices, such as toothbrushes and mobile phones. These systems typically allow energy transfer from a few watts to charge mobile phones up to a few kilo-watts to charge electric vehicles. Higher transmitted power levels typically require more extensive technical measures for safety and usually require a higher efficiency to comply with energy regulations. When charging an electric vehicle a wireless power transfer system must deliver a few kilo-watts of power to charge the battery in a reasonable time. In that case the efficiency usually must be higher than 90% to keep the generated heat and the additional power cost within limits. Also wireless power transfer systems designed for mobile phones are usually designed to provide a pretty good efficiency of up to 70% but also to provide a constant output voltage. However, neither such a high efficiency nor a constant voltage output and nor an output power as higher than 5 watt is needed to charge a battery of a low cost handheld device like a toothbrush or a shaver.
Accordingly, a need exists in the industry for a low cost charging system that realizes efficiency in the range of 15%-50% and provides power in the range of 250 milli-Watts and 5 Watts.